This invention relates to apparatuses for reducing bowing and warping in substrates during substrate bonding and methods of employing the same.
Bonding of multiple substrates is required to enable three-dimensional integration of semiconductor chips. Through-substrate-via (TSV) structures, formed after multiple substrates are bonded and optionally thinned, provide electrical connection across the multiple substrates in a bonded structure including at least two semiconductor substrates. The bonded structure can be subsequently diced to provide stacked chips. Each stacked chip includes a plurality of semiconductor chips stacked in the vertical direction with electrical connection therebetween.
Substrates are subject to local warping and bending due to internal stress. In the case of semiconductor substrates including many semiconductor devices composed of different semiconductor materials, insulator materials, and/or conductor materials and subjected to elevated temperatures during processing, the local warping and/or global bowing of the semiconductor substrates can be substantial. For example, for a semiconductor substrate with a 300 mm diameter and a thickness of about 800 microns, the radius of curvature of global bowing can be less than 100 m, which can generate a deviation of a surface of the semiconductor substrate from a nominally planar surface by a distance on the order of tens of microns.
The difficulty of bonding two semiconductor substrates having a local warping and/or a global bowing is illustrated in FIG. 1A. In FIG. 1A, a first semiconductor substrate 310 and a second semiconductor substrate 320 are brought into contact for bonding. Each of the first and second semiconductor substrates (310, 320) has a built-in global bowing. Unless the two semiconductor substrates have the same amount of global bowing in the same direction, some portions of the resulting bonded structure includes a gap between the two semiconductor substrates.
Further, semiconductor substrates to be bonded also have local warping as illustrated in FIG. 1B. The local warping of the semiconductor substrates is superposed to the global bowing of the semiconductor substrates. For example, the first semiconductor substrate 310 may have a first global bowing built in as schematically illustrated by a first global bowing curve 311, and the second semiconductor substrate 320 may have a second global bowing built in as schematically illustrated by a second global bowing curve 321. The variation superposed to the global bowing is the local warping of each semiconductor substrate (310, 320). In general, the combination of global bowing and local warping in each semiconductor substrate generates gaps in bonded structures employed to form stacked chips.
Presence of such a gap in a bonded structure of two or more semiconductor substrates presents difficulties in subsequent processing by preventing formation of continuous through substrate vias or by allowing unintentional ingress of materials during planarization or wet processing steps.